Identify Duplicate entry in a field

[windsurfit]

I would like to have an entry in a field note when there is a duplicate entry in another field. ie:

if a1 input is 12345 then b1 displays "date"
if a2 input is 12346 then b2 displays "date"
if a3 input is 12345 again then b3 displays "Duplicate Entry" and so on..

It would also be great if I could have that b3 field change font color when there is a duplicate?

Help always appreciated...

 

[just_jon]

One way, in B1, copied down:

=IF(MATCH(A1,A$1:A1,0)=ROW(),"date","Duplicate Entry")